Primary design considerations for a VSAT geostationary satellite telecommunication network include the cost of the remote terminal (VSAT) as a function of its complexity, the bandwidth efficiency as determined by the access scheme, and the communications delay as a function of the distance to the satellite. VSAT networks typically have two basic network configurations, the "star" configuration and the "mesh" configuration, with each configuration having important implications regarding cost, efficiency, and delay.
In a star network each inbound message from a VSAT is transmitted via satellite to a hub station, being the center of the star network, which then directs the message to its destination, usually to an external terminal, the hub station itself, or another VSAT. In a star network, when one VSAT sends a message to another VSAT the message is transmitted twice via satellite, and is referred to as having traveled two "hops," one from the source VSAT to the satellite and then to the hub (first hop), and another from the hub back to the satellite and then to the destination VSAT (second hop). With each hop an additional delay is added to the communication. A long delay is particularly undesirable in voice telecommunication where a delay is most noticeable between two VSATs The VSAT in a star network is relatively inexpensive, mainly because the hub station has a large satellite dish and powerful amplifiers that allow for simple and inexpensive RF VSAT components such as small antennas, commercial LNBs, and simple transmitter devices. Synchronization of VSATs is relatively simple as all VSATs listen to the hub station's outbound carrier, therefore timing "ticks" on the outbound transmission or any other similar method may be used.
In a mesh network any VSAT can communicate directly with any other VSAT in the network directly through a satellite without the need for an intermediate hub to relay messages between the VSATs, thus the delay is only one hop. In a mesh network the hub station is generally used to manage satellite resources such as allocating frequencies and performing Monitor & Control functions.
The VSAT in a mesh network is generally more expensive than the VSAT in a star network because of the former's ability to communicate with other VSATs and because there is no large antenna with which the VSAT communicates, such as the hub has in a star network. VSATs in a mesh network, therefore, generally require larger antennas and more powerful and stable RF front ends (i.e., LNBs, SSPAs, etc.) due to the symmetrical nature of the network and the link budget. Synchronization of VSATs is relatively complicated since each VSAT needs to acquire a time base from hub burst transmissions, which might be sparse and bursty, thus adding to the complexity and cost of a VSAT.
The hub-to-VSAT portion in a star network is usually more efficient than the same link in a mesh network as this link in a star network is continuous and may support multiple simultaneous communications efficiently by employing silence removal algorithms.
Some VSAT satellite telecommunications networks provide one or more links to a terrestrial network, such as a public switched telephone network (PSTN). In a star network this connection is usually located at the hub, and in a mesh network it can be at any VSAT as well. Multiple links to the PSTN at different locations would reduce the cost and delay of calls being made from the satellite network to the terrestrial one and vice-versa.